In 1951 he returned to the United States, and after serving in the U.S. Army, settled in Washington, D.C., where he began to teach, in 1953. The following summer, he enrolled in a summer institute at Catholic University, studying under Kenneth Noland. He became a friend of Noland, who became a significant influence on Downing's art and who was one of the founders of the Washington Color Field Movement.

His paintings to a large extent consisted of circles arranged in precise patterns on the canvas, with colors often chosen according to ideas of symmetry. Downing's Spot Paintings are his best known works.[3]

In the last ten years of his life, Downing lived in Provincetown, Massachusetts. He died in October 1985 in Provincetown, Massachusetts at the age of 57. In its obituary the Washington Times characterized his death as mysterious. The newspaper was referring to the then recent demise of Washington Color Field artist Gene Davis (1920–1985) and to the earlier death of Howard Mehring (1931–1978), as well.[4]